Enhancing Ammonia Power Generation: A Study on Integrated System Designs Using PEMFC and Other Technologies

EFCF 2025: Fuel Cells, Electrolysers & H2 Processing 1 - 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17244109 A0701 Page 1/12 A0701 Enhancing Ammonia Power Generation: A Study on Integrated System Designs Using PEMFC and Other Technologies Antonin Bruneau* (1,3), Du Wen (2), Xinyi Wei (1,2), Aris Maroonian (3), Jan Van Herle (1) (1) Group of Energy Materials (GEM), Ecole Polytechnique Fédérale de Lausanne, 1950 Sion/Switzerland; (2) IPESE, EPFL Valais Wallis, 1950 Sion/Switzerland; (3) Neology Hydrogen SA, 1095 Lutry/Switzerland; *Contact corresponding authors: www.EFCF.com/ContactRequest Abstract Ammonia is recognized as a non-carbon alternative for hydrogen storage and transport, noted for its efficiency, cost-effectiveness, and safety. At the heart of utilizing ammonia in power generation through fuel cells is the ammonia cracking process (ammonia to hydrogen to power), which requires temperatures above 500°C to release hydrogen. This study explores the integration of ammonia crackers with different power generation technologies, including traditional internal combustion engines (ICE), low-temperature proton exchange membrane fuel cells (PEMFC), and high-temperature solid oxide fuel cells (SOFC). Through modelling and system level optimization in ASPEN and AMPL, this study models and refines how each technology, combined with an ammonia cracker, performs, incorporating components like hydrogen catalytic burners, membranes, and heat exchangers to assess each scenario’s benefits and limitations. This approach highlights the benefits of utilizing ammonia crackers in an "ammonia-to-hydrogen-to-power" pathway compared to a more direct "ammonia-to-power" route without cracking. While findings indicate that SOFC offers the most efficient integration, achieving a global efficiency of 76.9%, albeit with a need for careful temperature control strategies, PEMFC can achieve a global efficiency of 54%, when carefully selecting the technology through system optimization. The study proposes a new system layout that not only utilizes ammonia—a clean, non-carbon fuel—but also enhances efficiency through compact PEMFC design solutions. This approach offers promising pathways for deploying ammonia in a variety of energy systems using PEMFC, highlighting its potential for cost-effective scalable, clean power generation. Figure 1. Systems configurations EFCF 2025: Fuel Cells, Electrolysers & H2 Processing 1 - 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17244109 A0701 Page 2/12 1. Introduction: The global reliance on fossil fuels undermines long-term energy security and sustainability. Since carbon fuels dominate, sourcing must be reassessed. Although renewable hydrogen production is expanding, many regions lack the resources to generate it efficiently. Ammonia (NH₃) emerges as a promising hydrogen carrier due to its high energy density, existing infrastructure, and easier transport. Cracking imported ammonia provides hydrogen without costly liquefaction, enabling a global hydrogen economy. This expands supply chains, enhancing energy security. Developing ammonia cracking technologies is thus essential— not only to unlock clean hydrogen, but also to enable dispatchable power generation. When integrated with electricity production, these systems can stabilize grids and serve as backup during outages, offering a carbon-free alternative to diesel generators. Unlike batteries, ammonia-based systems are scalable and suitable for large-scale applications, making them key assets for achieving carbon neutrality. This supply chains, enhancing energy security. However, ammonia requires conversion via cracking. A variety of ammonia-to-power conversion technologies have been investigated, including conventional systems, internal combustion engines (H2ICE), as well as emerging technologies like solid oxide fuel cells (SOFC) and proton exchange membrane fuel cells (PEMFC). This study analyzes ammonia-based energy conversion, assessing efficiency, cost, and viability to guide future research and industry applications. 1.1 Ammonia cracking for hydrogen production The transition from fossil fuels is essential for long-term energy sustainability. Hydrogen is a promising clean fuel due to its high energy density and zero emissions [1], but storage and transport challenges limit its adoption. Ammonia, a hydrogen carrier, offers advantages in storage and economic feasibility. Lan et al. analyzed hydrogen-ammonia energy conversion, finding hybrid storage most cost-effective, with an NPV of 39.31 million USD and LCOE of 0.81 USD/kWh [2]. Efficient hydrogen extraction from ammonia is crucial. Cho et al. studied ammonia cracking, showing that Ru catalysts improved reaction kinetics and achieved 99.99% hydrogen purity [3]. Makhloufi et al. analyzed large-scale ammonia decomposition, achieving 68.5% thermal efficiency and projecting hydrogen costs to drop to 3 USD/kg by 2040 [4]. Advancements in catalysts, heat recovery, and process integration remain key to scaling ammonia cracking for hydrogen supply. 1.2 Hydrogen purification in ammonia cracking Ammonia cracking produces hydrogen-rich gas containing residual impurities, requiring purification before use. Common separation methods include PSA and membrane separation, each balancing purity, recovery, and scalability. Membrane separation offers continuous purification with lower energy demands. Jo et al. developed a Pd/Ta membrane reactor, achieving 99.9% hydrogen purity at 450 °C under 6.5 bar ammonia feed, improving ammonia conversion efficiency to 99.5% [5]. 1.3 Ammonia-based power generation technologies Ammonia-derived hydrogen can fuel power generation systems. Roy et al. developed a fluidized bed reactor for ammonia decomposition, optimizing conditions at 2 bar and 550 °C to enhance hydrogen yields for gas turbines, where lean combustion (H2 < 20%) improved efficiency [6]. Zhang et al. highlighted that internal combustion engines (ICEs) require lower hydrogen purity than fuel cells, making onboard ammonia cracking cost-effective (4.50 USD/kg vs. 6.66 USD/kg for liquid hydrogen) [7]. Wang et al. studied ammonia/hydrogen fuel mixtures in ICEs, showing that a 30% hydrogen blend at 476K improved combustion EFCF 2025: Fuel Cells, Electrolysers & H2 Processing 1 - 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17244109 A0701 Page 3/12 stability but excess hydrogen (>50%) increased NOX emissions, necessitating optimized blending strategies [8]. Solid oxide fuel cells (SOFCs) can operate directly on ammonia, leveraging hightemperature decomposition (600–1000 °C) into hydrogen and nitrogen. Wan et al. found ammonia-fed SOFCs achieved up to 57% efficiency, comparable to hydrogen-fed SOFCs, but anode degradation from nickel nitride formation remains a challenge [9]. Elmutasim et al. reported that SOFCs achieved their highest power density at 650°C, with hydrogen spillover improving reaction kinetics, although nickel nitridation limits performance [10]. Sánchez et al. compared direct ammonia-fed SOFCs with hydrogen carriers, finding that direct use led to higher conversion losses and material degradation, with electricity production costs at 1200 EUR/MWh [11]. Mukelabai et al. examined a power-to-ammonia-to-power (P2A2P) system, integrating reversible solid oxide cells (rSOC) with the Haber-Bosch process, achieving a round-trip efficiency of 41–53% and power-to-hydrogen efficiency of 80% [12]. These studies highlight SOFCs’ potential for ammonia-based energy solutions, though efficiency improvements and material optimizations remain key challenges. Proton exchange membrane fuel cells (PEMFCs) offer a viable option for ammonia-derived hydrogen use, requiring high-purity hydrogen but providing lower operating temperatures and faster startup than SOFCs. Their study found that producing hydrogen from ammonia (0.54 USD/kg) was significantly cheaper than storing pure hydrogen (14.95 USD/kg), reinforcing ammonia's role in a circular hydrogen economy. Rathore et al. compared SOFC and PEMFC, highlighting that SOFC can directly use ammonia, achieving 50% efficiency, surpassing gas turbines (31%) and internal combustion engines (21%) [13]. However, SOFC faces material degradation due to ammonia decomposition by-products, necessitating anode stabilization strategies. PEMFCs, despite requiring hydrogen separation, offer flexibility and rapid response, making them better for decentralized applications, while SOFCs are more suited for stationary power generation with higher efficiency but greater degradation risks. 1.4 Gaps and contributions Ammonia is a promising energy carrier due to its ease of storage, transport, and diverse production pathways, but its economic feasibility varies by region [14, 15]. Prior studies have not fully addressed the impact of technology selection on system efficiency and costs. This study formulates ammonia-to-power (A2P) pathways, evaluating different cracking, purification, and power generation technologies, including, H2ICE, PEMFC, and SOFC. Instead of identifying a single optimal pathway, it highlights trade-offs based on technoeconomic performance, providing insights for industry decision-making. Additionally, it examines how technology readiness levels (TRL) and scalability affect ammonia’s role in future energy systems. Key contributions include assessing ammonia’s competitiveness, optimizing A2P system efficiency, and identifying major factors influencing the levelized cost of electricity (LCOE). 2. Materials and methods This section first defines the scope and boundaries of the work. Then, it introduces the technologies involved and the specific details needed to construct process models. Finally, in the scenario analysis, all configurations are evaluated using key performance indicators. 2.1 System description Figure 1 illustrates the schematic diagram for Ammonia-to-Power (A2P) pathway. Ammonia is imported from countries that offer competitive prices for green ammonia because of their EFCF 2025: Fuel Cells, Electrolysers & H2 Processing 1 - 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17244109 A0701 Page 4/12 abundant renewable energy resources and capabilities for large-scale transportation. A pump raises the liquid ammonia to the desired pressure before it is vaporized and heated to reach the necessary temperature for cracking into hydrogen and nitrogen. At the exhaust of the cracker, a gas scrubber removes unreacted ammonia using water, with the stripped ammonia either recovered or treated as wastewater. The resulting hydrogen and nitrogen are then separated using membrane technology. The retentate flow is burned in an afterburner to supply heat. The produced hydrogen can be used in internal combustion engines (ICE) or fuel cells (PEMFC or SOFC) to generate electricity and heat. While hydrogen purity requirements are less stringent for SOFCs, unreacted ammonia must be reduced to parts per million levels before entering PEMFCs to prevent material degradation. The off-gas is then directed to the afterburner for further combustion. The selection of specific technologies depends on their temperature and pressure requirements, ensuring optimal performance within the system. 2.2 System modeling 2.2.1 Ammonia cracker Imported ammonia at 25 °C and 10 bar is first pressurized using a pump to meet the required system pressure. It is then heated to 600 °C and directed to the ammonia cracker, where catalytic decomposition of ammonia occurs according to Equation (1). 2𝑁𝐻3→ 𝑁2+3𝐻2, Δ𝐻∘=92.44 kJ/mol (1) This endothermic reaction is highly temperature-dependent and requires elevated temperatures to ensure efficient conversion. Ammonia conversion increases significantly in the medium temperature range of 250–450 °C, with conversion approaching a plateau beyond 450 °C [16]. At such high temperatures, reaction kinetics become the dominant factor for achieving near-complete conversion. The detailed reactor configuration and catalyst selection are beyond the scope of this study. Instead, an RGibbs reactor model within ASPEN Plus V.11 [17] is employed to represent the maximum forward reaction progress. Experimental results from reference [18] confirm that equilibrium conversion is achievable above 450 °C. To ensure maximal conversion while maintaining a reasonable temperature, the simulation is performed at 600 °C. In addition, the reactor pressure is adjusted according to each scenario, depending on the use of a membrane or the pressure requirements at the inlet of the power conversion system. 2.2.2 Hydrogen separation and purification A membrane model is constructed based on Cechetto model [19]. Due to differences in pressure and concentration, the feed flow is pressurized and enters the membrane, where it divides into permeate flow and retentate flow. An analytical model has been developed to determine the permeate and retentate flows using Eq. (2)-(4). Assuming the ideal selectivity of hydrogen over nitrogen and ammonia. It was decided that the minimum partial pressure difference between the retentate and the permeate should be 1 bar, based on this the partial pressure at the exhaust of the retentate has been assessed, and then used to compute the hydrogen recovery factor. 𝐻𝑅𝐹 = 𝐻2,𝑟𝑒𝑐𝑜𝑣𝑒𝑟 󰇗 𝐻2,𝑝𝑟𝑜𝑑𝑢𝑐𝑒 󰇗 (2) 𝑃𝐻2,𝑟𝑒𝑡 𝑜𝑢𝑡 =(√𝑃𝑝𝑒𝑟𝑚 +√2−1)2 (3) 𝐻𝑅𝐹 =1−(1 𝑋𝐻2 𝑖𝑛 −1)𝑃𝐻2,𝑟𝑒𝑡 𝑜𝑢𝑡 𝑃𝑟𝑒𝑡−𝑃𝐻2,𝑟𝑒𝑡 𝑜𝑢𝑡 (4) Furthermore, the required membrane surface area is calculated based on the hydrogen flux in the permeate, the pressure difference across the membrane, and the membrane’s EFCF 2025: Fuel Cells, Electrolysers & H2 Processing 1 - 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17244109 A0701 Page 5/12 permeance, as shown in Eq. (5). Here the permeance is of 2.8e-4 mol. m−2.Pa−0.5, and the pressure in the retentate has been chosen to be 50 bar. 𝐴= 𝐻2 󰇗 (√𝑃ret−√𝑃perm)⋅Π (5) 2.2.3 Hydrogen power generation PEMFC, SOFC, and H2ICE are considered for power generation. Analytical models simulate the process, with the PEMFC model based on references [20, 21]. The reversible overpotential is estimated using the Nernst equation: 𝐸𝑃𝐸𝑀𝐹𝐶 = 𝐸0+𝑅𝑇𝑃𝐸𝑀𝐹𝐶 2𝐹 ln(𝑃𝐻2√𝑃𝑂2 𝑃𝐻2𝑂) (6) 𝐸0=1.299−0.000846(𝑇𝑃𝐸𝑀𝐹𝐶 −298.15) (7) where 𝐸𝑃𝐸𝑀𝐹𝐶 is the reversible overpotential, 𝑇𝑃𝐸𝑀𝐹𝐶 is the working temperature, and PH2,PO2,PH2O are partial pressures. Overpotential losses affect the actual voltage, and power generation is determined as: 𝑃𝑃𝐸𝑀𝐹𝐶 =(𝐸𝑃𝐸𝑀𝐹𝐶 −𝐸𝑙𝑜𝑠𝑠)𝐽𝑃𝐸𝑀𝐹𝐶𝐴𝑃𝐸𝑀𝐹𝐶 (8) 𝐽𝑃𝐸𝑀𝐹𝐶𝐴𝑃𝐸𝑀𝐹𝐶 =2𝐹𝑁𝐻2 (9) where 𝐽𝑃𝐸𝑀𝐹𝐶 is current density, 𝐴𝑃𝐸𝑀𝐹𝐶 is membrane area, and NH2is hydrogen consumption rate. A single-pass fuel utilization rate of 83% is assumed. The SOFC model follows a similar analytical approach [22], with no strict hydrogen purity requirement. Cooling water and swept air regulate temperature, and 80% of exhaust gas is recycled. The overpotential loss of the PEMFC is 0.42V and the one of the SOFC is 0.16V. For H2ICE, high-purity hydrogen is pressurized to 20 bars and injected into the combustion chamber, achieving an optimal brake thermal efficiency of 40% [23]. 2.2.4 Energy recovery The ammonia cracker operates at high temperatures (600 °C), producing gases with significant recoverable energy. Waste heat from SOFC, burners, ICE is also utilized to improve efficiency. This study applies a heat exchanger network (HEN) to optimize heat management, based on a framework from a previous study [24]. A mixed-integer linear programming (MILP) model is developed to minimize energy consumption and determine the optimal utility network using heat cascade equations and pinch analysis. The framework first assesses waste heat, converting it into usable energy [25]. 2.3 Scenario analysis Table 1 outlines the different system configurations considered in this study. The wellestablished PEMFC technology is compared with the emerging SOFC alternative. PEMFCs require high-purity hydrogen and minimal ammonia contamination, making a scrubber necessary between the cracker and the fuel cell. In contrast, SOFCs are more tolerant to variations in inlet gas composition but are generally more expensive than PEMFCs. The study also considers hydrogen internal combustion engines (H₂ICE), where hydrogen is burned in a combustion chamber. These systems offer the advantage of being retrofitted from existing infrastructure EFCF 2025: Fuel Cells, Electrolysers & H2 Processing 1 - 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17244109 A0701 Page 6/12 Scenario name Hydrogen to power conversion technology Membrane Burner S1 ICE No No S2 ICE Yes Yes S3 PEMFC No Yes S4 PEMFC Yes Yes S5 SOFC No Yes S6 SOFC Yes Yes Table 1. Different configuration for ammonia to power pathway Technical and economic key performance indicators are utilized to identify optimal configurations and are compared with competitors in the market: Energy efficiency: η𝑒𝑙𝑒 =𝑃𝑜𝑢𝑡 𝑚NH3LHVNH3 (10) Where η𝑒𝑙𝑒 is the system energy efficiency when producing hydrogen; 𝑚𝑁𝐻3 is the mass flow rate of the consumed ammonia, 𝑘𝑔.𝑠−1; LHV𝑁𝐻3 is the lower heating value of ammonia, 𝑀𝐽.𝑘𝑔−1. 𝑃𝑜𝑢𝑡 is the electricity produced, kW. Levelized cost of electricity (LCOE): 𝐿𝐶𝑂𝐸 =𝐶𝐶𝐴𝑃𝐸𝑋𝐶𝑅𝐹+𝐶𝑂𝑃𝐸𝑋 𝑃𝑜𝑢𝑡ℎ (11) 𝐶𝑅𝐹 = 𝑖(1+𝑖)𝑛 (1+𝑖)𝑛−1 (12) where 𝐶CAPEX is the capital expenditure of the system, USD; 𝐶𝑅𝐹 is the capital recovery factor; 𝐶OPEX is the operational expenditure of the system, USD; ℎ is the annual operating hour, h; 𝑖 is the discount rate; n is the lifetime of the system. All the value used in for the LCOE calculation are presented in table 2. EFCF 2025: Fuel Cells, Electrolysers & H2 Processing 1 - 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17244109 A0701 Page 7/12 Name Value Unit Ref. Operating hour per year 5246 hr [-] Discount rate 6 % [-] Maintenance and manpower 5% of CAPEX [-] PEMFC system cost 1200 USD/kW [26] Lifetime of PEMFC 10000 hr [27] SOFC system cost 10000 USD/kW [28] Lifetime of SOFC 40000 hr [28] ICE cost 1000 USD/kW [29] Lifetime of ICE 80000 hr [30] Membrane cost 20000 USD/kW [31] Lifetime of membrane 3 y [32] Catalyst cost 4000 USD/kg [33] Lifetime of Catalyst 5 y [-] Reactor Frame cost 10000 USD/kgH2/h [-] Lifetime of reactor frame 25 y [-] Ammonia supply system 1000 USD/kgNH3/h [-] Lifetime of ammonia supply system 15 y [-] Ammonia price 1.32 USD/kg [34] Table 2. Used value for LCOE calculation 3. Results and discussion Figure 2 presents the energy conversion efficiencies for each scenario (calculated in accordance with Equation 10), along with the conversion technology employed ICE for Scenarios S1 and S2, PEMFC for S3 and S4, and SOFC for S5 and S6. The table also includes the ammonia consumption per kWh of electricity produced. It is evident that the scenarios involving SOFC technology exhibit significantly higher efficiencies compared to the other cases. Scenario S6, in particular, achieves an efficiency of 76.5%, which is markedly superior to the values attainable with alternative technologies. This performance can be attributed to two primary factors: the inherently higher efficiency of the SOFC compared to the PEMFC (74.5% vs. 65.0%), and the elevated operating temperature of the SOFC (750°C). This high-temperature operation enables the recovery and valorization of thermal losses within the system—specifically, by utilizing the available heat to drive ammonia cracking at 600°C—an approach that is not feasible with the lowertemperature PEMFC systems. Furthermore, it is noteworthy that in scenarios involving SOFCs, the ammonia-to-power efficiency exceeds that of the hydrogen-to-power pathway (76.5% vs. 74.5% in S6), underscoring the benefit of integrating hydrogen production directly within the power generation system. EFCF 2025: Fuel Cells, Electrolysers & H2 Processing 1 - 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17244109 A0701 Page 8/12 Conversely, the scenarios based on ICEs are the least energy-efficient, with efficiencies of 30.8% and 25.5% for S1 and S2, respectively. This is consistent with the generally low conversion efficiency associated with internal combustion engines. Among the PEMFC-based scenarios, S3 achieves a higher efficiency than S4. In S3, the absence of a membrane results in lower fuel cell efficiency and reduced hydrogen consumption (as gas recirculation is not feasible). However, the unconsumed hydrogen is routed to the afterburner, where it is combusted to produce heat that can be utilized elsewhere in the system—thus enhancing the overall system efficiency. In contrast, Scenario S4 involves nearly complete hydrogen consumption within the PEMFC, leaving less residual hydrogen available for heat recovery. As a result, additional electrical energy must be used to supply the heat required for ammonia cracking, leading to a reduction in overall system efficiency. Figure 2. Ammonia consumption, Ammonia and hydrogen to power efficiency Figure 3 illustrates the Levelized Cost of Electricity (LCOE) for each scenario. A notable observation is the varying contribution of capital expenditures (CAPEX, shown in blue) and operational expenditures (OPEX, shown in yellow) across the different technologies. ICEbased scenarios (S1 and S2) exhibit lower capital costs and longer operational lifetimes, but this is counterbalanced by their low efficiency, which leads to higher ammonia consumption (as shown in Figure 2) and thus higher OPEX. The resulting LCOE values are 1.113 USD/kWh for S1 and 0.977 USD/kWh for S2. For PEMFC scenarios, the improved efficiency reduces OPEX, and although the technology's limited lifespan increases CAPEX, the overall LCOE remains favorable. The LCOE for S3 is 0.655 USD/kWh, while that of S4 is 0.848 USD/kWh. In the case of SOFC-based systems, the high efficiency yields a low OPEX. However, the high capital cost and shorter lifetime of SOFC components significantly impact the CAPEX. Consequently, the LCOE values are 0.744 USD/kWh for S5 and 0.731 USD/kWh for S6. S1 S2 S2 prime S3 S4 S5 S6 NH₃ consumption kg/kWh 0.733 0.655 0.655 0.358 0.426 0.272 0.252 Ammonia to power efficiency 0.255 0.308 0.308 0.548 0.451 0.714 0.765 Hydrogen to power efficiency 0.4 0.4 0.4 0.514 0.650 0.665 0.745 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 EFCF 2025: Fuel Cells, Electrolysers & H2 Processing 1 - 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17244109 A0701 Page 9/12 Figure 3. Levelized cost of electricity for the different scenario 4. Conclusions The costs of PEMFC and SOFC technologies can be reduced, and their operational lifespans extended through ongoing research and development. These advancements would lower capital expenditure (CAPEX) and, in turn, reduce the levelized cost of electricity (LCOE). However, both fuel cell technologies still face limitations in terms of maturity and market availability, which currently hinder their large-scale deployment. Today, fuel cells typically do not exceed power outputs of 200 kW, making internal combustion engines (ICE) more relevant for higher power applications. In contrast, hydrogen internal combustion engines (H₂ICE) have reached a high technology readiness level (TRL) and benefit from widespread availability, making them a pragmatic short-term solution despite their lower efficiency. Each technology offers distinct advantages depending on the use case. SOFCs provide high efficiency and are ideal for continuous, stable power generation, though they suffer from long startup times and limited load flexibility. PEMFCs respond quickly and manage dynamic load changes well, making them suitable for systems with intermittent or variable power demands. ICE systems, while less efficient, offer rapid startup and high responsiveness to load variations, making them suitable for backup or fluctuating demand scenarios. Ultimately, the priority should not lie in selecting one specific technology, but in deploying systems that are more cost-effective than diesel, to support a viable energy transition. While SOFCs and PEMFCs hold greater long-term potential for higher efficiency and lower costs, H₂ICE remains a valuable near-term option, especially in regions where ammonia is affordable and higher power outputs are required. Rather than identifying a single “best” technology, the real objective is to combine all viable solutions—SOFC, PEMFC, and H₂ICE—depending on application needs. Used together, they offer a flexible and robust pathway to replace diesel generators and significantly reduce greenhouse gas emissions. 0.000 0.200 0.400 0.600 0.800 1.000 1.200 S1 S2 S3 S4 S5 S6 Levelized cost USD/kWh Maintenance NH3 SOFC PEM ICE Burner Membrane Reactor Frame Catalyst NH3 supply system